Fossils and Dating

Fossils and Dating

by Josie Castillo

​Objectives

At the end of this lesson you should be able to:

1. ​Explain what information fossils can reveal about ancient life;

2. And differentiate between relative dating and radiometric dating.

​Before we start, let's see if you can still recall the lessons you have reviewed from the CK-12 Self Paced Lessons

​Get ready!

Multiple Choice

What are solid evidences that provide information to show evolution had taken place.

• Fossils

• Artifacts

• Cave Paintings

• Rocks

Multiple Choice

What do you call the fossils that have been discovered?

• fossil discoveries

• fossil records

• fossil mummifications

• fossil anecdotes

Multiple Choice

Which of the following is FALSE about the evolution of horses as provided by fossils?

• They became taller, which would help them see predators while they fed in tall grasses.

• They evolved a single large toe that eventually became a hoof.

• Hooves helped them run swiftly and escape predators.

• Their molars (back teeth) became longer and covered with cement so that they can chew meat properly

Multiple Choice

What do you call scientists that deal with fossils?

• archaeologists

• paleontometrist

• paleontologist

• historian

​Fossils

• Evidences of evolution.​

• ​Paleontologists are scientist that study fossils.

• ​Index fossils, are forms of life which existed during limited periods of geologic time and thus are used as guides to the age of the rocks in which they are preserved. (e.g., Cambrian Period = Paradoxides pinus

​Dating

• ​In geological terms, dating means to determine the age of a rock or fossil.

​Absolutely not the one you see in that funny comic strip...

​Before we start, let's see if you can still recall the lessons you have reviewed from the CK-12 Self Paced Lessons

​Get ready!

Multiple Choice

What do you call the process of using the concentrations of radioactive substances to estimate the age of a material?

• Objective Dating

• Subjective Dating

• Radiometric Dating

• Relative Dating

• A

Multiple Choice

Which of the following is NOT a kind of radiometric dating?

• Carbon-14

• Potassium-Argon

• Uranium-Lead

• Superpositioning

Poll

Which kind of rock can you not use radiometric dating?

• Igneous

• Sedimentary

• Metamorphic

• Folliated

​Two Kinds of Dating

• Relative

• ​establishes the relative age of fossils.

• ​can only tell if the rock/fossil is young or old but not the exact age.

• uses index fossils to estimate age of rocks or fossils.

​It is kind of similar to generation labels, the generation labels are your index fossils. If you are a millennial, gen-z, then you must be young

​Kinds of Relative Dating

• Stratigraphy is the technique used in relative dating.

• Laws of stratigraphy can help scientists understand Earth’s past.

• ​Stratigraphy is usually credited to a geologist from Denmark named Nicolas Steno.

Nicolas Steno was a Danish scientist, a pioneer in both anatomy and geology who became a Catholic bishop in his later years.

Law of Superposition​

• New (young) rock layers are always deposited on top of existing rock layers. Therefore, deeper layers must be older than layers closer to the surface. This the law of superposition.​

​Law of Original Horizontality

• ​Sediments were deposited in ancient seas in horizontal, or flat, layers. If sedimentary rock layers are tilted, they must have moved after they were deposited.

• ​If the layers are horizontal then the rocks are younger there. If it has sloping (due to folds) then the rocks there are older.

​Law of Lateral Continuity

• Rock layers extend laterally, or out to the sides. They may cover very broad areas, especially if they formed at the bottom of ancient seas. Erosion may have worn away some of the rock, but layers on either side of eroded areas will still match up.

​Law of Cross-Cutting Relationship

• ​Cross-cutting relationships is a principle of geology that states that the geologic feature which cuts another is the younger of the two features. It is a relative dating technique in geology.

​Unconformities

• ​Geologists can learn a lot about Earth’s history by studying sedimentary rock layers. But in some places, there’s a gap in time when no rock layers are present.

• A gap in the sequence of rock layers is called an unconformity.

• ​James Hutton discovered and named the term unconformity.

Hutton's unconformity, in Scotland.

​The discovery

​Hutton's discovery was a very important event in geology! Hutton determined that the rocks were deposited over time. Some were eroded away. Hutton knew that deposition and erosion are very slow. He realized that for both to occur would take an extremely long time. This made him realize that Earth must be much older than people thought. This was a really big discovery! It meant there was enough time for life to evolve gradually.

​Summarizing

Multiple Choice

Let's try this. Which rock would be the youngest?

• A

• B

• B

​The answer is B

​Why?

​It follows the Law of Cross Cutting Relationship. The geologic feature which cuts another is the younger of the two features. B cuts through A and C. Hence, making it the youngest layer.

​

Multiple Choice

Which is the oldest layer?

• B

• D

• E

• C

Multiple Choice

Which is the youngest layer?

• B

• D

• E

• A

​The answer is C for the 2nd question and A for the last one.

​It follows both cross cutting and superpositions.

​Cross cutting tells us that A is the youngest next to is is B, so on until C.

​Making C the oldest.

​Two Kinds of Dating

​Absolute/Radiometric Dating

• ​determines a fossil’s approximate age in years by finding the proportion o radioactive to nonreactive isotopes in a sample.

• ​isotopes - are two or more types of atoms that have the same atomic number and position in the periodic table, and that differ in nucleon numbers due to different numbers of neutrons in their nuclei.

• ​Radioactive isotopes in fossils and rock layers decay, or break down, at a steady rate, called a half-life. They are reactive because they decay. Nonreactive isotopes either take longer to decay or do not decay at all.

​Here are kinds of common isotopes that are used in Radiometric Dating/Absolute dating

TIP: You must remember which types of material they date and the age range they can do.

​Limitation

• It is not very useful for determining the age of sedimentary rocks. For sedimentary rocks, scientists use nearby igneous rocks that can be dated to get a general time frame​

Multiple Choice

Which type of carbon isotope can be used for dating?

• C-14

• C-12

• C-15

Multiple Choice

Which materials can be dated by C-14/ Carbon-14 radiometric dating?

• Crystals

• Organic remains

• Igneous Rocks

• Minerals

​Wrapping that up!

• ​Let us have a short recitation, choose a question, think of your answer and raise your hand when you are ready to answer:

• Why is it important for geologists to date fossils / rocks? What do we, non-geologists do with their information?

• ​How different is absolute dating from relative dating?

Poll

Rate Yourself! On the scale of 1 (needs more studies) to 4 (can totally date rocks)

How well did you do with the objectives mentioned in the introduction?

Objectives: ​Explain what information fossils can reveal about ancient life;

And differentiate between relative dating and radiometric dating.

• I can explain a little information given by fossils but I need more studies for dating fossils and rocks

• I can explain the information given by fossils but I need more practice when it comes to dating fossils and rocks.

• I can explain the information given by fossils and I know how to define but not differentiate the two types of dating rocks.

• I can explain everything that I have learned about fossils and differentiate relative from radiometric dating.

​REMEMBER! ANNOUNCEMENTS!

• ​Pointers for Finals:

• ​Pedosphere

• ​Hydrosphere

• ​Fossils and Dating

​

​Always check your Google Classroom for updates or, wait for your presidents' announcements. You can also send emails to [e-mail] if you have any concerns, suggestions or comments. There is always a plenary before the start of all classes. Remember to always attend and sign the log in and log out attendance.